The Baltimore Pediatric AIDS Clinical Trials Group (PACTG) reflects a long-standing collaborative effort between the Departments of Pediatrics of Johns Hopkins University (JHU) School of Medicine and the University of Maryland Baltimore (UMB). Established in 1988, the Baltimore PACTG has provided HIV-infected children and pregnant women in Baltimore and throughout the state of Maryland with access to clinical trials. More than 500 women and children have been enrolled in PACTG trials since the inception of the Unit. Over 300 perinatally HIV infected children are currently in active clinical follow-up at the two sites, as well as 60 HIV infected adolescents whose risk factors are limited to sexual and drug use exposure. Approximately 50 HIV infected women deliver per year at the two hospitals. This collaborative effort has brought together investigators with considerable scientific expertise in the areas of clinical trials, perinatal HIV transmission, medication adherence and HIV virology. Baltimore PACTU investigators have participated actively in PACTG leadership roles, currently serving on 10 PACTG committees/protocols. In addition, the two units have developed a broad range of international collaborations with mid-level and developing countries, both through independent research funding, as well as through the Fogarty AIDS International Training and Research Program (AITRP), HIV Prevention Trials Network (HPTN) and HIV Vaccine Trial Network (HVTN). In this submission, we have strengthened our adolescent component, adding investigators with strong track records in both the science and conduct of research among adolescents, including a newly funded Adolescent Medicine Trials Network for HIV/AIDS Interventions (ATN). With our existing infrastructure and broad scientific expertise, we anticipate continuing to enroll participants into a variety of protocols and making substantial contributions to the PACTG scientific agenda.